The present invention relates in general to the field of wireless communications and more particularly to a method and apparatus that provides spatial diversity within an indoor network.
The background of the invention is described in connection with wireless communications in an indoor network environment having multiple access points to the network backbone.
At present, Wireless Local Area Networks (xe2x80x9cWLANsxe2x80x9d) provide multiple access points with a point-to-point Radio Frequency (xe2x80x9cRFxe2x80x9d) connection for access to network systems. At high data rates, the network environment contains multi-path nulls which inhibit full data-rate communications and require significant processing to mitigate. In addition, many users compound the problem by increasing the background interference level. A major cause of these problems is that the access points operate independently and perform primitive hand-offs amongst users.
At the same time, third generation cellular standards (xe2x80x9cCDMAxe2x80x9d), such as CDMA 2000, ESI, ARIB, etc., are enabling private access points for wireless data communications using private, indoor base stations for data rates up to 2 Megabits per second (xe2x80x9cMbpsxe2x80x9d). Generally, the mobile station is comprised of a hand-held communicator placed in close proximity to the computing device (coupled to each other via infrared link), or a PCMCIA card inserted into the notebook computer.
A common technique used to separate several devices in a wireless environment is to spread the data by convolving a symbol for each character that identifies the base station from which it originated. For example, a data rate of 2 Mbps corresponds to a chipping rate of 4 Mega Chips Per Second (xe2x80x9cMCPSxe2x80x9d) wherein each data character is represented by a symbol that is 2 bits long, i.e. 2 chips per bit.
Compared to normal voice communications which code up to 128 chips per bit (an 8 kilobyte per second voice data channel) third generation cellular systems typically use relatively short codes, which are known as Walsh codes, for mobile station segregation and identification. Such coding schemes are prone to data errors especially in very high capacity network environments where each base station is associated with a single code. While error correction and data recovery algorithms can be used to improve data integrity, such methods tend to decrease throughput, create bottlenecks or in some cases result in loss of data.
Thus, signal interference tends to increase with the amount of data traffic. In heavily utilized business environments where several hundreds telephones and notebook computers may be operated, reliable error-free communications may be impossible.
In addition, since cellular networks were originally designed for outdoor use, CDMA modulation techniques do not specifically address the problems unique to multi-path interference due to enclosed walls and ceilings. Present day CDMA standards are optimized for outdoor communication where the objects (reflectors) are very large. Indoor environments have many more reflections of small delay which confound the spreading code used for outdoors. For example, while an echo (multipath) may be understood by a human as an indications of being in a large room, a mobile computing device such as a notebook computer may mistake the same multipath (echo) as originating from some other device on the network.
WLAN devices permitting wireless access to network connections are available. Such devices typically include a RF transceiver card that interfaces with the computing device which in most cases is a notebook computer. A similar device is attached to or placed near a network access point permitting bi-directional communications between the computer and other network components.
Such WLAN devices are limited, however, to a range of about 50 meters. Moreover, such devices do not typically control the power in their antennas and, as such, cannot support a large number of mobile computers in a single network environment. For example, many WLAN transceivers sets limit the number of mobile computers to 4 or 5 units in a 50-meter cell.
Another limitation associated with present day WLAN systems is that they use carrier frequencies which are largely unregulated and available for use by a wide array of consumer electronic equipment such as microwave ovens at 2.45-2.50 Ghz and cordless phones which employ a carrier frequency of either 900-928 Mhz or 2.4-2.482 Ghz. Thus, the potential for signal interference with consumer electronics in these bands is high and unpredictable.
Third generation cellular systems will include downlink data rates of at least 2-Mbps utilizing very weak CDMA techniques known as short Walsh codes. These weak ( less than 64 bit) codes will not permit effective mitigation of interference from other users and multi-paths in the indoor environment.
Accordingly, disclosed is a method and system of determining the spatial distinctiveness of a plurality of computing devices within a wireless networked environment. A signal is transmitted from a mobile computing device to a group of access points (APs) within the network as opposed to a single AP. Each access point receives the signal and converts it to its digital equivalent for digital processing. The converted signal is sampled and reduced to a set of vector data that is aligned in amplitude and phase to create a vector matrix specific to the communicating device.
Over-sampling of the converted digital signal ensures enough resolution to enable precise spatial determination of the computing device depending on the phase difference of the signal with respect to each access point. The vector data is aligned in time and mathematically combined to achieve a unique set of vector points for each mobile computing device. Thus, communication during movement of the computing device is made possible since multi-path communications are enhanced using the spatial representation of all computing devices on the network. Even when the device is fixed in space, the environment is ever changing due to moving people, equipment and doors.
In another embodiment, the aligned vector matrix is forwarded to other network components using the network interface and established network protocols. Since the same data is transmitted to and received by several APs, the vector matrix permits a determination as to whether a signal is emanating from a desired location (constructive interference) or from some other source of interference (destructive interference).
In yet another embodiment, a network data signal is distributed to several APs after modification by the vector alignment matrix. Multiple APs transmit the amplitude and phase modulated waveform which constructively converges on the space occupied by the deserved mobile transceiver.
Also disclosed is an architecture for providing network-level spatial diversity using multiple indoor access points. A transceiver is coupled to a user""s portable computer or similar mobile computing device. Signals from the computing device are received by more than one access point on the network. The incoming signals are sampled and aligned to permit calculation of the phase and amplitude differentials at each point as a function of time. The phase and amplitude data are stored in the network to create a vector matrix for the computing device which can be updated continuously as the computing device is moved from one location to another within the network environment. A code can be assigned to the vector matrix that is associated with the computing device. In this way, all signals within the network can be associated with a specific network component as a function of the component spatial orientation. Other aspects and advantages of the invention including its specific implementations are understood by reference to following detailed description taken in conjunction with the accompanying drawings.